(1) Field of the Invention
The present invention relates to a dispersing and grinding apparatus for finely grinding materials and dispersing them into liquid by means of a grinding medium such as balls, beads, etc.
(2) Background Information
It is supposed that a dispersing and grinding apparatus, which has a plurality of discs or agitating blades disposed within a vessel to disperse a material, applies centrifugal force to a mixture of a grinding medium and the material by rotation of the discs, circulates the grinding medium between the discs, during which the grinding medium captures the material, and disperses the material by shearing forces. However, the flow characteristic of such a mixture is not uniform throughout the vessel. For this reason, the flow of the grinding medium often causes a short pass or dead space, whereby it is difficult to obtain uniform shearing forces. Although it has been known to provide an inner cylinder within a vessel of a dispersing and grinding apparatus to apply motion to the grinding medium by rotation of the inner cylinder, such a technique does not always effect movement of the grinding medium at approximately equal velocity throughout the inner cylinder.
The present inventors have proposed a dispersing and grinding apparatus having a rotor disposed within a vessel and having a guiding means disposed on the periphery of the rotor for controlling the flow of the grinding medium. Such an apparatus is disclosed in U.S. Pat. No. 4,919,347. It has been confirmed that, according to the dispersing and grinding apparatus described in the aforesaid patent, a material-grinding medium mixture flows through a narrow, annular flow path between the rotor and the vessel by guiding means in the form of an array of forward guide surfaces and an array of rearward guide surfaces in a manner which approximates a plug flow, and flows around the periphery of the rotor without causing the formation of high velocity gradients. Since then, the present inventors have investigated various structures as the above-mentioned guiding means, and also studied a structure in which protrusions and grooves are disposed in the axial direction of the rotor in the shape of a toothed wheel. However, in such a structure, the mixture which enters the grooves of the rotor causes a velocity difference in the axial direction, and the mixture tends to advance straight toward the outlet from the inlet of the vessel so that sufficient dispersion effect sometimes cannot be obtained.